The present invention relates to a method for moulding thermoplastic compositions. In a preferred form, the invention relates to the moulding of liners or gaskets in container closures.
Hitherto it has been known for example when forming a liner for a container closure to pre-heat the thermoplastic material and to mould the heated and thus softened material using a mould die which is not itself heated and may even be positively cooled so that in either case it presents a relatively cool moulding surface. However, the above described moulding process involves a considerable dwell time of the thermoplastic material in an oven, through which closures carrying metered quantities of the plastics material, are passed along a tortuous conveyor path. Such a system is, for example, disclosed in our British patent application No. 5948/73 in which the heat is imparted to the thermoplastic material by radiation within the oven. This has the disadvantage that, if for any reason the movement of the closure-carrying conveyor through the oven stops, the closures in the oven rapidly become overheated and "scorched" with the result that they are unsuitable for use.